Phytoplankton community structure in relation to physico-chemical factors in a tropical soda lake, Lake Shala (Ethiopia)

Phytoplankton communities responses to physico-chemical factors were studied in Lake Shala from January to December 2018. Distinct spatial and seasonal variations were observed for all physico-chemical parameters, except DO (ANOVA: p < 0.05). In total, 72 taxa, Bacillariophyta (55 taxa), Chlorophyta (seven taxa), Cyanobacteria (six taxa), Euglenophyta (two taxa), Dinophyta (one taxon) and Charophyta (one taxon) were identified. Phytoplankton abundance and biomass ranged from 5 789.3 cells ml–1 to 1 516.2 cells ml–1, with a mean of 8 756.9 cells ml–1 and 9.8 μg l−1 to 25.8 μg l−1, with a mean of 17.1 μg l−1, respectively, and showed seasonal variations (p < 0.05). Based on RDA analysis, most species were abundant in Shala Gike Shore station. Their distribution was negatively correlated with salinity and EC, whereas pH, alkalinity, NO3–N, SRP, TP, NH3–N and SiO2 had a positive correlation. Previously Lake Shala was dominated by Cryptophyta but this has switched to a diatom-dominant community. Such changes in phytoplankton taxa may be suggestive of ecological change. This study provides baseline data on the phytoplankton community structure of Lake Shala associated with physico-chemical changes, against which future community structure can be evaluated.